I've just made an elliptical coffee table, which I hope Pete is going to shoot in a couple of weeks. Here is an extract from the article I have written about it. It assumes you have a piece of MDF big enough to make the template, onto which are marked both centre lines and diagonals:
Then clamp another board to [the workpiece], with its square corner at the centre of the template. Next take a length of timber, say 20x10mm in section and drill a hole for a pencil at one end. From the centre of this hole drill two more, to take nails, one which is half the length of the ellipse from the pencil and one which is half the width of the ellipse from the pencil. Insert nails into these holes. Now you simply lay this stick onto the board and swing it, keeping the nails in contact with the two edges at all times. The pencil will describe a quarter of an ellipse accurately, directly onto the MDF. By repositioning the clamped board, the other 3 quadrants can be drawn. Carefully bandsaw and sand the ellipse.
Another way of drawing and ellipse is to put two nail in and wrap a loop of string around them and a pencil. Then, keeping the string taught draw around the nails with the pencil. The relative length of the string and the distance between the nails determines the ellipticality (sic) of the finished ellipse.
Not sure if that is clear but shout if it isn't and I'll try again.